F. Eugeni, R. Mascella, D. Pelusi
All logic instruments and tools in possession of, and used by researchers are generally considered as the results of bivalent logic. A common error to people interested in science is that, usually, they don’t known with certainty which things are true and which are false. But they are sure that things are true or false. No ways in the middle. The fuzzy principle asserts that this is completely a question of measure. Fuzziness is the opposite concept to bivalency, while fuzzy quality means polyvalency. Fuzzy logic is able to manage uncertain knowledge and, more precisely, to manage those rules difficult to formalize. In many cases, such rules havent got, or cannot have, the necessary precision, required for a whole formalization. 2. Reasoning and fallacies The reasoning is a process by means of which human beings put in action their thought, and particularly their abstract thought. One of the more important tasks in logic is, therefore, to explain correct methods of the thought. The reasoning concept can be regarded like a set of proposal that stand independently one from the others, and takes into account the temporal order of involved events.